Aberrant methylation in the promoter of tumor-related genes is associated closely with epigenetically mediated gene silencing. The aim of the present study was to evaluate the methylation profile of Tunisian nasopharyngeal carcinoma (NPC) and to determine the clinicopathological features of tumors showing this epigenetic alteration.
Thirty-six archival NPC biopsies were investigated in comparison with 19 non-tumor nasopharyngeal tissue specimens. DNA methylation status of ten tumor-suppressor and related genes was analyzed by using methylation-specific PCR. The Epstein-Barr virus (EBV) presence was verified by PCR and in situ hybridization and the LMP1 oncoprotein expression was analyzed by immunohistochemistry. Findings were then correlated with clinicopathological variables (Patients' gender and age, tumor histological subtype and stage).
Hypermethylation frequencies of the investigated genes in NPC biopsies were 75% for RASSFIA, 58.3% for SHP1, 47.2% for DAPK, 33.3% for P16, 31% for RARβ2, 19.4% for GSTP1 and TIMP3, 11% for APC and CDH1, and 5.5% for MGMT. In non-tumor nasopharyngeal samples, hypermethylation was detected in lower frequencies in 6 genes (SHP 26.3%, P16 21%, RARβ2 21%, DAPK 15.8%, TIMP3 10.5%, and GSTP 5.3%). Hypermethylation of RARβ2 promoter was more frequent in tumors with lymph node metastasis than those without metastasis (43.5% vs 0%, p=0.03). Methylation of RASSF1A was more frequently detected in non-keratinizing NPC than in undifferentiated subtype (100% vs 66.7%; p=0.05). A trend toward positive association was found between an increased number of methylated genes and LMP1 expression (p=0.07). However, no significant association was found for the remaining variables.
This study indicates that hypermethylation of multiple genes is a common alteration in nasopharyngeal carcinomas in Tunisian patients and that this epigenetic change may play a role in the nasopharyngeal carcinogenesis.